In the manufacture of hydrophilic (“soft”) ophthalmic contact lenses, it is conventional to package each manufactured lens in a disposable package for containing a single lens and predetermined amount of liquid (generally buffered saline). Typically, the lens and liquid are introduced to a cavity or well in a container. The container is usually formed from a thermoplastic (e.g., molded polypropylene or polystyrene). After the lens and liquid are placed into the container, the container is sealed by applying a foil strip to the top of the container to form a lid and heat sealing the strip to the top of the container to form a package. The heat sealed package containing both the lens and liquid is then subjected to further processing, including for example, sterilization.
Conventional apparatus used for the high speed packaging of contact lenses on an assembly line is designed to permit inspection and packaging of several contact lenses simultaneously. Typically, a plurality (generally 6, 8 or 10) of containers are mounted in a fixed carrier rack having a cavity for receiving each container. A contact lens and liquid are introduced to each container mounted on the rack. The rack of containers is then conveyed to an inspection station where each container is inspected to ensure that a contact lens is present and not defective. The rack then moves onto a platen in a heat sealing station where a preformed sheet of foil stock is positioned over the rack of containers. A heated mandrel is then applied to the rack to apply predetermined heat and pressure for a predetermined time, thereby heat sealing the foil stock to each container and forming sealed packages. As a result, each of the containers is now each heat sealed to the sheet of foil stock and is accordingly joined together to form multi-package arrays. The foil stock is provided with perforations to permit the packages to be separated from each other after further downstream processing and/or shipping.
The packaging approach described above presents several disadvantages. For example, by providing a plurality of lens containers on each rack, the detection and identification of a defective or missing lens on the rack at the inspection station is complicated. A complex matrix tracking system must be employed to identify which container or containers on the rack has failed inspection and track them through the process until they can be removed.
Another problem inherent in processing multiple containers simultaneously in a fixed rack arrangement is that each container on the rack is subjected to identical heat sealing conditions. Due to variations in the molding process, the molded thermoplastic containers sometimes vary in height. In such an event, a container of non-standard height may be subjected to either too little pressure (if too short) or too much pressure (if too tall) compared to the pressure experienced by a container of standard height. As a result, the heat seal formed on one or more of the array of packages joined together by the perforated foil sheet may be of unacceptable quality. One defective heat seal in the array will require that the entire array of packages be discarded, and, thus, an entire production lot may be subject to further testing for heat seal failures, which, if present, may require rejecting the entire production lot.
Finally, in the prior art heat sealing apparatus, the sheet of perforated foil stock is positioned over the rack of containers upstream of the heated mandrel station. This arrangement relies on gravity and friction to maintain the lidstock in position until the heat seal is formed. Slight lateral movement of the foil stock causes mis-registration of the stock on the set of containers and could result in a defective set of packages.
The apparatus described above is disclosed in U.S. Pat. No. 5,687,541 issued to Martin et al. Other packages and packaging apparatus systems are disclosed in U.S. Pat. No. 5,649,410 issued to Martin et al., U.S. Pat. No. 5,561,970 issued to Edie et al., U.S. Pat. No. 5,094,609 issued to Kindt-Larsen, U.S. Pat. No. 4,691,820 issued to Martinez, U.S. Pat. No. 5,620,087 issued to Martin et al., U.S. Pat. No. 5,749,205 issued to Edwards et al. and U.S. Pat. No. 5,577,367 issued to Abrams et al. Each of the references cited herein are incorporated by reference. In the event of conflict in the meaning or interpretation of the present specification and/or appended claims, the present specification controls.
It will be apparent that there continues to be a need for an apparatus capable of detecting and selectively removing failed containers. In addition, the need exists for a heat sealing apparatus capable of applying a predetermined amount of pressure to each container in a group of containers being sealed simultaneously. Finally, there is a need for a heat sealing apparatus that is capable of maintaining a sheet of lidstock in registration with the set of containers during heat sealing. There is also a need for a sealing apparatus that is sensitive to angular irregularities in container heights, and discrepancies in the planes of the platen and the surfaces of the heat seal dies, and one that can provide for more consistent heating of the heat seal dies. The present invention addresses these needs.